2000 Pontiac Bonneville Speed Sensor going wrong

Hello, I have a 00' Bonneville with more than 150000 miles. Recently I forced my transmission too much n broke it. I had to replace it, and given the miles on my car I didn't think it was worth getting a reconstructed tranny. So instead I purchased a used 00' Buick Lesabre tranny and swapped it. Actually the mechanic did. After the swap my speed sensor was bad so I replaced it. Five mile into driving the sensor goes bad or something because my sppedometer doesn't mark my speed, tranny shifting is not smooth, and sometimes I get stuck on 1st gear. I think all this is due to the sensor because I've tried replacing it like three times in a Row. Service Engine Soon still comes up with Bad Speed Sensor, Any reasonable suggestion would be fine thank you.